Cold valve lash with aluminum heads will measure about .006 greater when they heat up so when the engine is fresh you set the lash at .006 tighter cold to get started. Always lash the engine hot for an accurate final setting. The head will expand at different rates along the head due to thermal mass and unequal heating which is the condition that the engine runs in. Always do the lash and check it at the same temp every time. The hotter temp that you set them at the tighter they will be when cold.
Bruce